In highway construction, the use of crash attenuators has seen increased use due to rising liability costs, congestion of highways and the need for expanding present road systems without closing them to traffic. These crash attenuators are utilized on abutments, bridge columns and even on the rear of parked construction and maintenance vehicles.
One type of attenuator that has seen widespread use in recent years is a truck mounted attenuator which is operable to be disposed on the rear of a sand truck that is utilized by a road crew. This truck is typically utilized as a barrier at the rear of the construction project. Therefore, if a vehicle fails to notice warning signs indicating ongoing construction, the vehicle will impact the rear of this truck having the attenuator mounted thereon. The attenuator will absorb the impact, both preventing damage to the truck and the individuals that may be occupying the truck, and also minimize damage to the impacting vehicle.
These previous truck mounted attenuators have utilized an enclosure which is mounted on a lift on the rear bumper of the truck. This lift is operable to dispose the attenuator in either a horizontal position or in a vertical position. In the horizontal position, the attenuator extends outward and rearward of the truck. The attenuator is comprised of an enclosure in which elongated hexagonal shaped cells are disposed. The walls of these cells are fabricated of a lightweight aluminum and are oriented such that the longitudinal axis thereof is horizontal to the ground. This provides the maximum compression forces for relatively lightweight material. Although these cells are only filled with air, some applications of these hexagonal cells have utilized a foam filling.
The hexagonal cells have typically been fabricated from a non-corrosive material and disposed in a sheet metal or aluminum housing. When the housing is impacted, it ruptures and allows the rear face thereof to move forward into the impact absorbing material to cause it to compress. This compression is what provides the energy absorption, thus decelerating the impacting body.
Another type of crash attenuator has been fabricated from the solid block of foam. The foam is covered with an outside enclosure and then mounted on a lift on the rear of the vehicle. Typically, the enclosure for this type of attenuator is comprised of fiberglass. One disadvantage to this type of structure is that when the compressed attenuator has been impacted with a vehicle, the fiberglass has a tendency to shatter, thus hurling fragments in many directions. This could result in a safety hazard.
One disadvantage with present crash attenuators is the material which is utilized internal to the enclosure. When an aluminum hexagonal cell material is utilized, this can result in the possibility of corrosion, in addition to the expense of fabrication. The external enclosure, while allowing moisture to leak out, can result in a safety hazard when the enclosure ruptures.